For continuous production of desired moldings by an injection molder, plasticized synthetic resin is injected from the cylinder of the molder through the nozzle into the cavity of a mold connected to the nozzle. In such continuous molding, it is essential to inject plasticized synthetic resin by the amount corresponding precisely to the inside capacity of the cavity, in other words, the volume of an intended product. If the injected amount is greater than required, the resin is forced out through the parting line of the mold to form flash. On the other hand, if the injected amount is less than required, recesses or sinks are formed on the molded surface, resulting in a defective product.
Conventionally, for continuous production of moldings with a stable quality, the amount of plasticized synthetic resin injected to fill the mold cavity is detected on the basis of the position of the screw in the injection molder, as described in the following:
i) The injected amount is detected on the basis of the screw position before the plasticized synthetic resin is injected into the mold cavity. ii) The injected amount is detected on the basis of the following screw position upon completion of dwelling after the plasticized synthetic resin is injected into the mold cavity.
1) The position of the screw at the forward limit for dwelling PA1 2) The position of the screw released from the dwelling pressure after dwelling is completed.
However, both of these conventional methods have a problem that the detection may not be accurate because of the following reasons: